The present invention relates generally to methods of connecting an electromagnetic interference (EMI) shield to a printed circuit board (PCB) of an electronic device. In particular, the present invention relates to different shield design techniques, features and the use of secondary connector components to efficiently and effectively connect one or more EMI shields to a printed circuit board.
All electronic products emit electromagnetic radiation, generally in the range of 50 MHz to 3 GHz, but not limited to this range, especially considering the recent advances in high-speed microprocessor design and the rapidly increasing capabilities of high-speed networking and switching. The problem of emittance of electromagnetic radiation is not new to designers of electronic equipment; indeed, significant efforts are taken to reduce electromagnetic interference, electrostatic discharge, radio frequency interference (hereinafter referred to collectively as “EMI”) and virtually every country has a regulating agency (FCC in the U.S., for instance) that restricts the marketing and sale of electronic equipment that do not pass stringent requirements for EMI, whether radiation or intercepted (also called susceptibility) by an electronic device.
Present day solutions for EMI shielding generally include the use of conductively painted plastic housings, conductive gaskets, and metal cans that are affixed to the printed circuit board by soldering or similar methods, some of which are semi-permanently attached to the printed circuit board. In virtually all cases, however, the existing solutions are expensive and add significant costs to providing electronic equipment such as cellular phones, personal digital assistants (PDA), laptop computers, set-top boxes, cable modems, networking equipment including switches, bridges, and cross-connects, among a multitude of other electronic products.
In an effort to bring costs down while increasing EMI shielding, various technologies utilizing metallized polymer substrates have been developed for use as an effective EMI shielding solution. For example, U.S. Pat. No. 5,811,050 to Gabower, the complete disclosure of which is incorporated herein by reference, has provided a shielding approach wherein a thermoformable substrate (any number of polymers) is first thermoformed and then metallized. This approach offers the advantage of eliminating any stresses that may occur during thermoforming to a metallized layer that is applied to the substrate prior to the forming process. The product has been shown to be a highly effective and a relatively low-cost method for providing effective EMI control (also called electromagnetic compatibility or EMC) for electronic products.
Utilizing formed plastic shields that have been metallized has proven to be an effective shielding method that reduces the cost and overall weight associated with shielding of an electronic device. However, since a polymer substrate is used to create these types of EMI shields, some of the common methods used to attach and locate more traditional, metal EMI shielding solutions onto a printed circuit board are not applicable for polymer based shields. For instance, EMI shields in the form of “metal cans” are commonly soldered into place on a printed circuit board. Soldering is a method of heating a metal material or alloy, having a low melt temperature, until it reaches a molten state. The molten solder is then applied to both the metal shield and usually an exposed ground trace on the printed circuit board simultaneously. Once the solder cools and re-solidifies it creates both a mechanical and electrical connection between the EMI shield and the printed circuit board. Soldering achieves two goals, a soldered shield is physically located and retained in a desired orientation and location, and the solder connection effectively grounds the EMI shield, which is desirable for effective shielding.
However, if this same solder technique is used in conjunction with a metallized plastic shield, the heat from the molten solder would damage the plastic substrate and potentially compromise the shielding effectiveness of the EMI shield. Therefore, alternative shield design techniques, features and the use of secondary components to efficiently and effectively connect one or more EMI shields to a printed circuit board must be created.